The remediation of ground and groundwater contamination has become an important issue in recent years, and due to its unique nature as being well below ground level and in many cases not readily removable has thus also presented unique challenges to efforts seeking to render contaminated sites safe for habitation, and/or to contain and prevent migration of contaminants to non-contaminated areas.
One example of ground contamination remediation is discussed in U.S. Pat. No. 4,435,292. In this method, perforated pipes and wells are inserted into the ground of a contamination site, wherein a number of the pipes and wells are pressurized and others are simultaneously evacuated to effect the transfer of flushing fluid through the soil to accelerate the removal of contaminants, and to prevent migration of the contaminants into other areas. The system is closed and pressurized at one end and evacuated at another end, for example, by evacuating ducts connected to a central manifold. Flushing fluid is then forced under pressure through the perforated pipes to be forced into contaminated earth to flush out any contaminants situated therein. The flushing fluid may be either liquid or gaseous, e.g. an inert gas such as nitrogen, or a reactive gas system which would react with the contaminant to form an inert or harmless chemical. This process, however, suffers from the need for costly inert flushing fluids and/or gases, or the danger of further polluting contaminated soil with non-reacted flushing solvent.
Another attempt at soil decontamination is described in U.S. Pat. No. 4,600,508, which is said to be an improvement over the method discussed above. In this method, a plurality of perforated pipes are connected to a supply header for distributing water under the force of a pump throughout a contaminated area. An additional set of perforated pipes which are connected to a return header withdraw the water circulated under pressure which contains contaminants from the ground. The contaminants are thereafter removed from the water, and the water recycled to the system.
Other methods are known which involve providing a circulation system for leaching contaminants from a vadose layer, the area directly above the water table in the earth, into the water table where they are recovered by a water removal well and a pump. Examplary of this method is U.S. Pat. No. 4,167,973.
Such water flushing and leaching processes as described above, however, suffer from poor water solubility of most organic contaminants resulting in non-efficient and costly recovery.
Other methods to alleviate soil and/or groundwater contamination employ the creation of a vacuum within a withdrawal well situated in a vadose zone. Air injected into the soil at various points surrounding the withdrawal well urge the flow of contaminants towards the withdrawal well where they are vaporized and thereafter collected in the well by vacuum suction. Examples of this method are described in U.S. Pat. Nos. 4,593,760 and Re.33,102.
A variation of the vacuum method mentioned above is discussed in U.S. Pat. No. 4,730,672 which discloses a method for removing and collecting volatile liquid contaminants from a vadose zone of contaminated ground by an active continuous closed-loop process in which a vacuum source in a perforated conduit in a withdrawal well situated in a contaminated vadose zone creates a reduced pressure zone to cause contaminants contained therein to vaporize and be drawn in to the withdrawal conduit for collection and disposal.
While effective for the removal of some easily volatilized liquid contaminants in the vadose layer, such methods have proved to be of limited value in the removal and disposal of many other common subsurface contaminants. Additionally, such methods are not useful for removal of contaminants situated below the water table in a saturated zone.
Accordingly, there is a need for a process that will rapidly and efficiently decontaminate hydrocarbon contaminated subsurface areas including both areas above and below the water table.